Fig. 3. Ephrin-A5 is primarily localized to forelimb mesoderm. (A) Cross-section through stage 15 embryo at forelimb levels, hybridized with probe for ephrin-A5 mRNA. Ephrin-A5 mRNA is present at apparently low levels in the dermomyotome (arrow) and in the limb mesoderm (*). nt, neural tube. (B-F) Confocal z-series stacks (8 µm) from vibratome sections stained with ephrin-A5 and Pax7 antibodies. (B) At stage 15, ephrin-A5 protein is found in the ventral dermomyotome (dm, arrow), in the dorsal neural tube (nt) and at very low levels in the limb mesoderm (l). (C) At stage 16, ephrin-A5 is found at low levels in the lateral dermomyotome (dm) and in the limb (l). (D) At stage 17, ephrin-A5 localizes to the surfaces of many limb mesoderm cells (b, boxed area) but is expressed at very low levels in proximal territory containing Pax7 muscle precursor cells (a, boxed area). Boxed areas are shown at higher magnification in Da and Db. Prominent ephrin-A5 expression is present in the developing nephric system (n). (E,F) Ephrin-A5 is strictly associated with the ventral portion of the limb at stage 19 and 23. v, ventral; d, dorsal.